Jumping Jack Flash weblog

New test with IR receiver/transmitter using sound card

Posted in Infrarossi by jumpjack on 30 settembre 2009

Some tests have been performed using an Asus EEEPC 701 4G to both sample and play remote control signals.

EEEPC looks to have an high capabilities sound card, which allows sampling up to 154000 Hz; this allows properly sampling the original 38000 Hz carrier rather than just its presence/absence.

Standard audio card sampling:

Asus EEEPC sampling:


Using this sample, some tests hav been performed to determine if, how and when the EEEPC is capable of controlling the TV set which the remote belongs to.

Results are weird: ONE single LED appear to be enough to control the TV set, but NOT using the original sampled signal; instead, an artificial signal made out of a 19000 Hz tone and “mixed” into a stereo signal made up of inverted signals is needed to properly control the TV set.




8 Risposte

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  1. Mark Fazzio said, on 31 marzo 2010 at 5:53


    Great tutorial! I was able to get the signal in Audacity, but I have a couple of questions:

    So we should stick to the older method you showed for creating these wav files then? I was able to create the IR receiver, and able to record in Audacity. However, I am not sure how long these signals have to be. How do you know how long to press the buttons on the remote for and how long the signals have to be? Do you have any sample files that you might be able to send so I could get a better understanding?



    • jumpjack said, on 31 marzo 2010 at 12:02

      You can know how long a signal has to be by looking at its replicas: record a signal for a couple of seconds, and you’ll see several occurrences of the same signal; as sometimes the first one is different from the next ones, you have to exactly compare first two “replicas”: if they’re actually the same, you’ll need to recreate just one, and the to add copies at the same time-distance the original replicas are.

  2. Mark said, on 14 aprile 2010 at 3:46


    My waves look like they have lines coming off the bottom of them, like interference or something.

    Check this image out:

    Weird Wave

    Did I do something wrong?

    • jumpjack said, on 14 aprile 2010 at 8:11

      Your wave is perfect, just ignore those “spikes” (it’s quite complex to explain them…)
      About the carrier wave, I used a sine, but I think it does not matter which waveform you use. The “unused parts” of the waveform are those “outside the main signal”; it looks like your image is showing exactly the significative part of the signal, having you cut away “not significant” part, i.e. silence and signal replicas.

      Anyway your picture shows an INVERTED signal: you can determine it as the signal is normally absent (first segment), then it should RAISE (but it falls in your image), so you have to associate carrier presence to each low-parts of your signal and no-carrier to high-parts.

  3. Mark said, on 14 aprile 2010 at 5:04

    Hey sorry, two more questions. These are pertaining to your first article, under step 3: Editing Waveforms

    1. Is the carrier wave also a square wave?
    2. You say to “delete unused parts of the waveform.” I’m a little unclear what that means, or how to determine an “unused” part of the wave.


  4. Mark said, on 16 aprile 2010 at 5:43


    I’m sorry for all these questions! I found this thread:


    I am really trying to figure this out. I built the emitter, connecting the LED’s in opposite like you said, and going to each channel of the 3.5mm stereo headphone jack. The ground goes to nowhere, not sure if that’s right. Do I need any resistors? Here’s a pic:

    And I took the file into Raw2LIRC and came up with this:

    But I don’t understand what you mean when you say to “call the unizeri.bat file” or to call “create.bat specifying as parameter the “creator file” (unizeri-raw, or unizeri-tv,… )”

    I’m sorry again if these questions seem stupid.. I am trying to get this to work on my HTC Hero and I’m assuming like most phones it does not have symmetrical audio output, right? I searched but couldn’t find anything..

    Thanks so much, I appreciate the rapid responses and hope you can help!!

    Best regards,

    Mark Fazzio

    • Mark said, on 16 aprile 2010 at 5:53

      Hey I just realized in the photo of the circuit that I have the wire going to ground from the one side of the LED’s. I have since switched it so the wire is going to the other channel:


  5. […] New test with IR receiver/transmitter using sound card […]

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